This invention relates to the structure of a joint between a metallic tubular member and a metallic annular part and a method of joining them, especially a joint structure and a method of joining a tubular member and annular parts which are designed to constitute a hollow machine component such as particularly a hollow cam shaft and a cam or cams thereon.
The use of hollow structures for machine components such as the cam shaft in an internal combustion engine has become common recently because of the strong demand for savings in material and the weight reduction of such components. As a means for achieving this, a technique is known according to which annular parts such as cams are mounted in position on a tubular member prepared in advance, and then the tubular member is expanded to join them.
Japanese Patent Publication No. 21,299/71 discloses a method in which a tubular member (a shaft tube) is passed through heated split cam and journal combinations (each cam having a shaft hole with splines), and then the shaft tube is expanded by a pressing member (die) to joint the annular parts securely to the shaft tube. With this method, however, since splines are formed along the full length of each cam and journal and the shaft tube is expanded after is has been forced into the parts, the shaft tube inevitably stretches axially to cause bending or a nonuniform wall thickness of the tube, so that it is impossible to join the parts (cams and journals) securely and correctly in the specified positions. It is also extremely difficult to fix the cams in their specified positions by making allowance for possible elongation of the shaft tube. This method, therefore, can not be applied to mass produced machine components.
A method has also been made known by Japanese Patent Publication No. 506/81 in which a shaft tube is forced through splined shaft holes of cams and then only the portion of the shaft tube corresponding to the splined section of each cam is expanded outward to obtain a secure joint. This method also has a low reliability, especially in respect of pull-out force, because engagement is provided at only a few places, and it also requires specific tools for splining, etc., and thus has a low productivity.
The present invention has solved these problems. It has for its object the provision of a structure for joining annular parts securely and accurately to a tubular member, and a method of forming such structure.
In order to attain the object of this invention, at least one serrated portion is provided on the inner periophery of each annular part, the serrated portions being designed to cut or bite into the outer periphery of a tubular member to which the annular parts are joined, each of the annular parts also having a planar portion facing other portions of the tubular members (portions that are not cut into), designed so that substantially no pressure is exerted on the planar portions of the annular parts when they are joined to the tubular member, and then said tubular member is deformed plastically and expanded to effect the desired joining of the annular parts and tubular member within specified dimensional tolerances.
An embodiment of this invention will be described below with reference to the accompanying drawings which illustrate the embodiment.